HERBICIDE injury can prove a challenge in sorghum if management recommendations aren’t heeded.

GRDC has released a short informative video outlining key considerations for growers when using metolachlor-based herbicides to minimise the risk of damage to sorghum seedlings.

Hosted by Independent Consultants Australia Network senior consultant Mark Congreve, the video details how metolachlor-based herbicides like Dual work, factors that affect the level of exposure to and metabolism of metolachlor within the germinating seedling, and the role of the Concep II seed safener.

“Post-emergent herbicide options to control grass weeds in sorghum are limited so most growers rely on pre-emergent herbicides to control weeds throughout the establishment phase and in solid planted crops, until crop competition from shading at row closure helps slow further weed germination,” Mr Congreve said.

“One of the most common pre-emergent weed control strategies in sorghum is to apply a metolachlor-based herbicide such as Dual which is taken up by the shoot and roots of both the emerging weed and sorghum seedlings.

“In the case of the weed seedlings, this is important for effective control, but in the case of sorghum it is critical that the crop can rapidly metabolise the herbicide to avoid crop injury.

“Under situations conducive to excellent establishment of sorghum, growers rarely see damage where label directions are followed. Where damage occurs, it is commonly associated with another compounding factor that reduces the seedlings’ ability to metabolise the herbicide.

“The seedling’s ability to metabolise the herbicide is increased by the use of the Concep II seed safener, but decreased by any stress on the seedling from waterlogging, low soil temperature, disease or insect damage, low seed vigour and germination percentage.”

Mr Congreve said it was also important to optimise seedbed preparation and planter setup to ensure the planting slot created in the soil was well closed and no furrow was left over the seed row which may concentrate herbicide over the seedling following rainfall.

“If we can achieve good seed emergence and growing conditions, generally the sorghum crops can tolerate the pre-emergent herbicides we use,” Mr Congreve said.

He said the use of the Concep II seed safener was essential to reducing sorghum injury by helping the seedling metabolise and detoxify the herbicide metolachlor more rapidly.

Concep II should be applied to the seed prior to planting and growers can either order pre-treated sorghum seed or treat their seed on-farm.

If applying on-farm, Mr Congreve urged growers to use high quality seed (high germination count and good seed vigour), apply Concep II at the correct rate, completely cover the seed and not to store the seed for extended periods of time before planting.